Unlike most behaviorally active peptides and proteins, the pituitary hormone prolactin (PRL) promotes the display of functionally significant, species-typical behavior patterns, such as parental behavior and migratory activity, in a variety of vertebrate species. The objective of this research project is to determine if these unique stimulatory effects of PRL are mediated by direct action of the hormone on the brain. The ability of PRL to maintain readiness to sit on eggs in ring doves (Streptopelia risoria) is an excellent system for exploring this question because this behavioral action of PRL has been well documented in previous PRL injection studies and in our own preliminary experiments. In addition, receptor binding studies conducted in my laboratory have established the existence of specific binding sites for PRL in ring dove brain, thus strengthening the rationale for exploring possible direct effects of PRL in the CNS. An experiment is therefore proposed to investigate the effectiveness of twice daily intracerebroventricular infusion of ovine PRL in maintaining the readiness of ring doves to display incubation behavior when tested after a 10-day period of isolation from mates, nests, and eggs. This experiment, together with concurrent research in my laboratory on PRL binding site regulation in ring dove brain, should contribute significantly to a further understanding of protein hormone action on vertebrate brain function and behavior. The data should also be valuable in evaluating the hypothesis that the behavioral effects of hyperprolactinemia and neuroleptic drug treatment in men and women are mediated in part by direct PRL action in the CNS.